Electronic device

ABSTRACT

An electronic device includes a circuit substrate, a bottom case, and a top case. The circuit substrate has a plurality of slits penetrating therethrough. The bottom case has a groove portion positioned at an inside surface of the bottom case such that edge portions of the circuit substrate are slidable and inserted into the groove portion. Besides, a plurality of pin-shaped protrusion portions is provided in the bottom case to be snib-fitted with the top case, and each protrusion portion has a plurality of locking portions at a tip end portion. Each protrusion portion elastically biases the circuit substrate toward the top side of the bottom case and presses the circuit substrate to a top surface of the groove portion by locking the locking portions to the circuit substrate after the locking portions are respectively inserted into the slits.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2011-287974filed on Dec. 28, 2011, the contents of which are incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to an electronic device in which acircuit substrate is accommodated in a case.

BACKGROUND

Conventionally, a circuit substrate accommodated in a case is fixed to avehicle for protecting an attachment element on the circuit substrate.JP-A-2011-166048 and JP-A-2005-317692 describe a structure without usinga fastener such as screw, so as to reduce a cost when the circuitsubstrate is fixed to the case.

The above structure basically includes a top case and a bottom case. Thecircuit substrate is inserted between the top case and the bottom case.A force for holding the circuit substrate is affected by an engagementstate between the top case and the bottom case, and thereby the circuitsubstrate may be loosely received in the top case and the bottom case.Since the circuit substrate cannot be strongly received, one of the topcase and the bottom case may be readily apart from the other one by anexternal force. Thus, a displacement may be caused, and the circuitsubstrate and the element may be affected by an oscillation applied tothe cases for a long time.

Further, an acceleration sensor or a gyro sensor may be attached to thecircuit substrate. For example, an acceleration sensor for twodirections is attached to an airbag electronic control unit (airbagECU). Since the sensor on the circuit substrate is for measuringparameters relative to movement applied to the vehicle, ano-displacement state is necessary to be maintained between thesubstrate and the cases. When the displacement occurs, the sensor cannotcorrectly measure the parameters, and an abnormality such as anerroneous detection may be caused. For example, a security device mayactivate when the security device should not be activated.

SUMMARY

It is an object of the present disclosure to provide an electronicdevice, in which a circuit substrate is fixable without using a fastenersuch as screw, while a displacement of the circuit substrate can beprevented.

According to an aspect of the present disclosure, an electronic deviceincludes a circuit substrate, a bottom case, and a top case. The circuitsubstrate is provided with an electronic circuit. The bottom case has anopening portion at a top side, and the bottom case receives and holdsthe circuit substrate. The top case has an opening portion at a bottomside, and is attached to the bottom case from the top side of the bottomcase. The circuit substrate has a plurality of slits penetrating throughthe circuit substrate. The bottom case has a groove portion positionedat an inside surface of the bottom case such that edge portions of thecircuit substrate are slidable and inserted into the groove portion.Besides, a plurality of pin-shaped protrusion portions is provided inthe bottom case to be snib-fitted with the top case, and each protrusionportion has a plurality of locking portions at a tip end portion. Eachprotrusion portion elastically biases the circuit substrate toward thetop side of the bottom case and presses the circuit substrate to a topsurface of the groove portion by locking the locking portions to thecircuit substrate after the locking portions are respectively insertedinto the slits.

As described above, the circuit substrate is slidable in the grooveportion of the bottom case, and the locking portions of the protrusionportions are respectively inserted into the slits. Because the lockingportions elastically bias the circuit substrate toward the top side ofthe bottom case and press the circuit substrate to the top surface ofthe groove portion, the circuit substrate can be fixed without using afastener such as screw.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present disclosurewill be more readily apparent from the following detailed descriptionmade with reference to the accompanying drawings. In the drawings:

FIG. 1A is a cross-sectional view showing an assembling state of anelectronic device, and FIG. 1B is a cross-sectional view showing theelectronic device after being assembled, which are taken along the lineI-I in FIG. 2 according to a first embodiment of the present disclosure;

FIG. 2 is a top view showing a top case of the electronic deviceaccording to the first embodiment;

FIG. 3 is a top view showing a bottom case and a circuit substrate ofthe electronic device according to the first embodiment;

FIGS. 4A and 4B are enlarged views showing a tip end portion of aprotrusion portion according to the first embodiment and anotherembodiment;

FIG. 5A is a cross-sectional view showing an assembling state of theelectronic device, FIG. 5B is a cross-sectional view showing anotherassembling state of the electronic device, FIG. 5C is an enlarged viewshowing the protrusion portion and a guide portion in another assemblingstate of the electronic device, and FIG. 5D is an enlarged view showingthe protrusion portion and the guide portion after the electronic devicebeing assembled, according to the first embodiment; and

FIG. 6A is a cross-sectional view showing an assembling state of anelectronic device, and FIG. 6B is a cross-sectional view showing theelectronic device after being assembled, according to a secondembodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described. In theembodiments, a part that corresponds to a matter described in apreceding embodiment may be assigned with the same reference numeral,and redundant explanation for the part may be omitted. When only a partof a configuration is described in an embodiment, another precedingembodiment may be applied to the other parts of the configuration. Theparts may be combined even if it is not explicitly described that theparts can be combined. The embodiments may be partially combined even ifit is not explicitly described that the embodiments can be combined,provided there is no harm in the combination.

Hereafter, an electronic device 1 according to embodiments of thepresent disclosure will be described with reference to the drawings.

First Embodiment

FIGS. 1A and 1B are cross-sectional views of the electronic device 1taken along I-I in FIG. 2. FIG. 1A is a cross-sectional view showing anassembling state of the electronic device 1, and FIG. 1B is across-sectional view showing the electronic device 1 after beingassembled, according to a first embodiment of the present disclosure

As shown in FIGS. 1A and 1B, the electronic device 1 includes a top case2, a circuit substrate 3, and a bottom case 4. Both the top case 2 andthe bottom case 4 are made of resin such as polypropylene (PP).

The top case 2 includes four leg portions 5, a plurality of guideportions 6, and a plurality of engagement portions 7. The leg portions 5are for fixing the whole electronic device 1, as shown in FIG. 2. Eachguide portion 6 is U-shaped so as to guide a protrusion portion 12. Eachengagement portion 7 engages with a hook 13 of the bottom case 4 whenthe top case 2 is assembled to the bottom case 4.

The circuit substrate 3 is a printed-circuit substrate board mountedwith a circuit element and a connector 8, and is held in the bottom case4. The circuit element may be an electronic circuit (not shown). Theconnector 8 is for connecting to the exterior. Four slits 9 are providedin the circuit substrate 3 to fix the circuit substrate 3 to the topcase 2.

The bottom case 4 includes a groove portion 10, four protrusion portions12 and six hooks 13, for example. The groove portion 10 is provided suchthat the circuit substrate 3 is slidable in the groove portion 10. Fourlocking portions 11 are provided at a tip end portion of each protrusionportion 12. As shown in FIG. 3, the locking portions 11 look likesquares viewed from top. In the example of FIG. 4A, each locking portion11 is shaped to expand outside of a surface of the protrusion portion 12in accordance with increase in distance from the tip of the protrusionportion 12. In this case, the thickness of the locking portion 11 may beset approximately in uniform. While the locking portions 11 arerespectively passed through the slits 9, the locking portions 11 arediameter-reduced to pass through the slits 9 by an elasticity ofresinous protrusion portion 12 including the locking portions 11, andthen return the original shape after being passed through the slits 9.The locking portions 11 are configured to have a snib-shape so as to beprevented from being taken out from the slits 9 after being passedthrough the slits 9.

An assembling method of the electronic device 1 according to the firstembodiment will be described.

The circuit substrate 3 is slid in and inserted into the groove portion10 of the bottom case 4. FIG. 3 is a top view showing an assemblingstate where the circuit substrate 3 is completely inserted into thebottom case 4. As shown in FIG. 3, the protrusion portions 12 of thebottom case 4 are provided at positions corresponding to the slits 9 ofthe circuit substrate 3.

The circuit substrate 3 is set by using jigs (not shown) contacting abottom surface of the bottom case 4 with a small area. A bottom endportion of the top case 2 may be lower than a bottom surface of thebottom case 4 as in the assembling state of FIG. 5C, or the leg portions5 may be positioned lower than the bottom end portion of the top case 2.Thus, the jigs are used for pressing the top case 2 sufficiently to thebottom case 4, and for preventing interference between the leg portions5, the top case 2, and a work table.

The top case 2 is covered and pressed from a top side of the bottom case4. As shown in FIG. 5A, the hooks 13 and a bottom portion 14 of the topcase 2 are deformed and bent by the elasticity of resin so that thebottom case 4 can be inserted into the top case 2. The bottom portion 14is provided to correspond to the hook 13. The tip end portion of theprotrusion portion 12 is guided along the guide portion 6 and is bent toa direction opposite to a protruding direction of the protrusion portion12. The guide portion 6 is provided in the top case 2 such that aninside surface of the guide portion 6 is U-shaped. The locking portions11 expand like an umbrella, before being passed through the slits 9.

As shown in FIG. 5B, when the top case 2 is further pressed and lowered,the locking portions 11 are deformed such that a projected area of eachlocking portion 11 projected in a moving direction decreases. That is,the locking portions 11 are deformed and contracted like an umbrella. Inthis case, the locking portions 11 can be passed through the slits 9.

As shown in FIG. 5C, after the locking portions 11 of the protrusionportion 12 are completely passed through the slit 9, each lockingportion 11 returns its original shape. In this case, a base surface 12 aof the protrusion portion 12 of the bottom case 4 contacts the top case2 and thereby the top case 2 cannot be lowered any more. Further,because the hook 13 is inserted into the engagement portion 7, thedeformation (bending) of the hook 13 and the bottom portion 14 isdisappeared. It is readily to confirm by a sound or a shock transmittedto a hand that the six hooks 13 are respectively inserted into theengagement portions 7 of the top case 2. It may also be confirmed fromappearance of whether the bending is disappeared.

Because the tip end portion of the protrusion portion 12 varies muchwhen the protrusion portion 12 is guided along the guide portion 6, theguide portion 6 are set to have a sufficient margin so that theprotrusion portion 12 can U-turn. FIG. 5C is a cross-sectional viewshowing an assembling state where the top case 2 is pressed to thelowest position. In the assembling state of FIG. 5C, the engagementportion 7 of the top case 2 and the hook 13 of the bottom case 4 are notfitted to each other.

When the pressure is disappeared, the protrusion portion 12 tends toreturn its original shape by the elasticity of resin. A returning forceof the protrusion portion 12 applies to the circuit substrate 3 towardthe top side of the top case 2 by the locking portions 11. As shown inFIG. 5D, the circuit substrate 3 contacts a top surface 10 a of thegroove portion 10, and a space is generated between the circuitsubstrate 3 and a bottom surface 10 b of the groove portion 10. Becauseof the returning force, the hook 13 is fitted to the engagement portion7 such that the top case 2 cannot be readily taken out from the bottomcase 4.

The circuit substrate 3 will always be pressed to the groove portion 10by the elasticity of the protrusion portion 12. Thus, the circuitsubstrate 3 can be fixed without using fastener such as screw, and canbe received in the bottom case 4 without a moving.

According to the first embodiment, the electronic device 1 includes thecircuit substrate 3, the bottom case 4, and the top case 2. The circuitsubstrate 3 is provided with an electronic circuit. The bottom case 4has an opening portion at a top side, and the bottom case 4 receives andholds the circuit substrate 3. The top case 2 has an opening portion ata bottom side, and is attached to the bottom case 4 from the top side ofthe bottom case 4. The circuit substrate 3 has the slits 9 penetratingthrough the circuit substrate 3. The bottom case 4 has a groove portion10 positioned at the inside surface of the bottom case 4 such that edgeportions of the circuit substrate 3 are slidable and inserted into thegroove portion 10. Besides, the pin-shaped protrusion portions 12 areprovided in the bottom case 4 to be snib-fitted with the top case 2, andeach protrusion portion 12 has a plurality of the locking portions 11 atthe tip end portion. Each protrusion portion 12 elastically biases thecircuit substrate 3 toward the top side of the bottom case 4 and pressesthe circuit substrate 3 to the top surface 10 a of the groove portion 10by locking the locking portions 11 to the circuit substrate 3 after thelocking portions 11 are respectively inserted into the slits 9.

As described above, the circuit substrate 3 is slidable in the grooveportion 10 of the bottom case 4, and the locking portions 11 of theprotrusion portions 12 are respectively inserted into the slits 9.Because the locking portions 11 elastically bias the circuit substrate 3toward the top side of the bottom case 4 and press the circuit substrate3 to the top surface 10 a of the groove portion 10, the circuitsubstrate 3 can be fixed without using a fastener such as screw. Inaddition, the circuit substrate 3 is protected by the top case 2 and thebottom case 4. The locking portions 11 may be respectively inserted intothe slits 9 by using fingers.

The top case 2 may further have a plurality of guide portions 6 providedsuch that the inside surface of each guide portion 6 is U-shaped. Theprotrusion portion 12 is protruded toward the top side of the bottomcase 4. When the top case 2 is assembled to the bottom case 4, aconfiguration in which the locking portions 11 are inserted into theslits 9 may be achieved by guiding and turning the locking portions 11along the guide portions 6 to the direction opposite to the protrudingdirection of the protrusion portions 12 to head for the slits 9. Thus,the electronic device 1 can be assembled for a small assembling hours.

Second Embodiment

According to a second embodiment, protrusion portions 12 are provideddifferently from the protrusion portions 12 in the first embodiment, asshown in FIGS. 6A and 6B. Specifically, the tip end portion of theprotrusion portion 12 is positioned at a direct top side of the slit 9and heads for a bottom side of the bottom case 4. Besides, the guideportion 6 of the top case 2 is also different from the shape of theguide portion 6 in the first embodiment. As shown in FIGS. 6A and 6B, abottom surface of the guide portion 6 declines from a base part 6 a ofthe guide portion 6 to an inner side surface 6 b of the guide portion 6.Except for the protrusion portion 12 and the guide portion 6, otherparts of the electronic device 1 according to the second embodiment maybe the same as the parts of the electronic device 1 according to thefirst embodiment.

When the top case 2 is pressed toward the bottom side of the bottom case4, the guide portions 6 guide the protrusion portions 12 to head for theslits 9 such that the protrusion portions 12 are respectively insertedinto the slits 9. As shown in FIG. 6B, when the top case 2 is completelyassembled to the bottom case 4, the locking portions 11 of theprotrusion portions 12 press the circuit substrate 3 to the top surface10 a of the groove portion 10. The hooks 13 are engaged with theengagement portions 7 such that the top case 2 cannot be readily takenout from the bottom case 4.

The circuit substrate 3 will always be pressed to the groove portion 10by the elasticity of the protrusion portion 12. Thus, the circuitsubstrate 3 can be fixed without using fastener such as screw, and canbe received in the bottom case 4 without a moving.

According to the second embodiment, the bottom surface of the guideportion 6 declines from the base part 6 a of the guide portion 6 to theinner side surface 6 b of the guide portion 6. The protrusion portion 12is provided in the bottom case 4 such that the tip end portion ispositioned at the direct top side of the slit 9 and heads for the slit9. When the top case 2 is assembled to the bottom case 4, the lockingportions 11 are inserted into the slit 9 because the protrusion portion12 is pressed toward the bottom side of the bottom case 4 along theguide portion 6.

Then, the circuit substrate 3 and the top case 2 can be fitted to eachother by pressing the top case 2 to the bottom case 4.

Such changes and modifications are to be understood as being within thescope of the present disclosure as defined by the appended claims.

The protrusion portion 12 may be inserted into the slit 9 by a fingerafter the circuit substrate 3 is slid in the bottom case 4. In thiscase, the top case 2 may be provided to protect the circuit substrate 3without a structure having a member such as the guide portion 6. Thus,the processing cost of die and mold for injection molding can bereduced.

As shown in FIG. 4B, the locking portions 11 may be provided in a mannerthat one locking portion 11 is placed at a side surface of theprotrusion portion 12. Alternatively, the locking portions 11 may beprovided in a manner that two locking portions 11 are respectivelyplaced at two opposing side surfaces of the protrusion portion 12.

The material of the top case 2 and the bottom case 4 is not limited tothe PP. Other resin may be used, such as polybutylene terephthalate(PBT), polyethylene-telephthalate (PET), polycarbonate (PC), ABS resin,or polymer alloy. The resin may be conductive grade, or may includefilling material such as glass fiber or carbon fiber. Further, thematerial of the top case 2 and the bottom case 4 may be different fromeach other.

According to a first aspect of the present disclosure, an electronicdevice includes a circuit substrate, a bottom case, and a top case. Thecircuit substrate is provided with an electronic circuit. The bottomcase has an opening portion at a top side, and the bottom case receivesand holds the circuit substrate. The top case has an opening portion ata bottom side, and is attached to the bottom case from the top side ofthe bottom case. The circuit substrate has a plurality of slitspenetrating through the circuit substrate. The bottom case has a grooveportion positioned at an inside surface of the bottom case such thatedge portions of the circuit substrate are slidable and inserted intothe groove portion. Besides, a plurality of pin-shaped protrusionportions is provided in the bottom case to be snib-fitted with the topcase, and each protrusion portion has a plurality of locking portions ata tip end portion. Each protrusion portion elastically biases thecircuit substrate toward the top side of the bottom case and presses thecircuit substrate to a top surface of the groove portion by locking thelocking portions to the circuit substrate after the locking portions arerespectively inserted into the slits.

As described above, the circuit substrate is slidable in the grooveportion of the bottom case, and the locking portions of the protrusionportions are respectively inserted into the slits. Because the lockingportions elastically bias the circuit substrate toward the top side ofthe bottom case and press the circuit substrate to the top surface ofthe groove portion, the circuit substrate can be fixed without using afastener such as screw.

According to a second aspect of the present disclosure, a bottom endportion of the top case may include a plurality of leg portions forattaching the electronic device to a subject. The top case may bepositioned to cover the bottom case.

Thus, the bottom case receiving and holding the circuit substrate can beassembled to the whole electronic device without contacting anassembling surface.

According to a third aspect of the present disclosure, the protrusionportion may be provided to protrude toward one of the top side and thebottom side of the bottom case. In this case, the protrusion portion canbe inserted into the slit by a finger or a tool, and the circuitsubstrate can be readily fixed to the bottom case without a fastenersuch as screw.

According to a fourth aspect of the present disclosure, the top case mayfurther have a plurality of guide portions provided such that the insidesurface of each guide portion is U-shaped. The protrusion portion may beprotruded toward the top side of the bottom case. The locking portionsmay be respectively guided along the guide portions and bent to thedirection opposite to the protruding direction of the protrusionportions to head for the slits, and may be respectively inserted intothe slits, when the top case is assembled to the bottom case. Thus, theelectronic device can be assembled for a small assembling hours.

According to a fifth aspect of the present disclosure, the bottomsurface of the guide portion may decline from a base part of the guideportion to an inner side surface of the guide portion. The protrusionportion may be provided in the bottom case such that the tip end portionis positioned at the top side of the slit and heads for a bottom side ofthe bottom case. The locking portions are respectively inserted into theslits due to the protrusion portions pressed toward the bottom side ofthe bottom case along the guide portions, when the top case is assembledto the bottom case.

According to a sixth aspect of the present disclosure, the circuitsubstrate may be provided with an acceleration sensor or a gyro sensor.In this case, the electronic device may be used as an airbag ECU, asensor substrate, or an electronic stability control ECU (ESC ECU).

While the present disclosure has been described with reference to theembodiments thereof, it is to be understood that the disclosure is notlimited to the embodiments and constructions. The present disclosure isintended to cover various modification and equivalent arrangements. Inaddition, while the various combinations and configurations, which arepreferred, other combinations and configurations, including more, lessor only a single element, are also within the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An electronic device comprising: a circuitsubstrate provided with an electronic circuit; a bottom case that has anopening portion at a top side, and receives and holds the circuitsubstrate; and a top case that has an opening portion at a bottom side,and is attached to the bottom case from the top side of the bottom case,wherein the circuit substrate has a plurality of slits penetratingthrough the circuit substrate, the bottom case has a groove portionpositioned at an inside surface of the bottom case such that edgeportions of the circuit substrate are slidable and inserted into thegroove portion, and the bottom case is provided with a plurality ofpin-shaped protrusion portions, each protrusion portion has a pluralityof locking portions at a tip end portion, and each protrusion portionelastically biases the circuit substrate toward the top side of thebottom case and presses the circuit substrate to a top surface of thegroove portion by locking the locking portions to the circuit substrateafter the locking portions are respectively inserted into the slits. 2.The electronic device according to claim 1, wherein a bottom end portionof the top case includes a plurality of leg portions for attaching theelectronic device to a subject, and the top case is positioned to coverthe bottom case.
 3. The electronic device according to claim 1, whereinthe protrusion portion is provided to protrude toward one of the topside and the bottom side of the bottom case.
 4. The electronic deviceaccording to claim 1, further comprising a plurality of guide portionsprovided in the top case such that an inside surface of each guideportion is U-shaped, wherein: the protrusion portion is provided toprotrude toward the top side of the bottom case, and the lockingportions are respectively guided along the guide portions and bent to adirection opposite to a protruding direction of the protrusion portionsto head for the slits, and are respectively inserted into the slits,when the top case is assembled to the bottom case.
 5. The electronicdevice according to claim 1, further comprising a plurality of guideportions provided such that a bottom surface of each guide portiondeclines from a base part of the guide portion to an inner side surfaceof the guide portion, wherein the protrusion portion is provided in thebottom case such that the tip end portion is positioned at a direct topside of the slit and heads for a bottom side of the bottom case, and thelocking portions are respectively inserted into the slits of the circuitsubstrate due to the protrusion portions pressed toward the bottom sideof the bottom case along the guide portions, when the top case isassembled to the bottom case.
 6. The electronic device according toclaim 1, wherein the circuit substrate is provided with an accelerationsensor or a gyro sensor.